Shift work and heavy lifting may reduce women’s fertility, study finds

Women who work at night or do irregular shifts may experience a decline in fertility, a new study has found.

Shift and night workers had fewer eggs capable of developing into healthy embryos than those who work regular daytime hours, according to researchers at Harvard University.

There was also a reduction of around 15 per cent in the number of eggs ready for fertilisation in women with jobs requiring heavy lifting, including nurses and interior designers, they said.
The study, which involved two groups of women undergoing IVF, examined egg quality among 313 women who had completed one IVF cycle as well as the total number of eggs in the ovaries of 473 women at a fertility clinic.

Co-author Audrey Gaskins told The Independent women whose jobs involved shift work or heavy lifting “had fewer eggs in total [that] the fertility specialists were able to retrieve. Among the eggs they were able to retrieve, a lower number were of good enough quality to progress further”.

While the scientists were unable to assess the potential impact of several factors including working hours, testosterone levels or childhood exposure to smoking on the participants’ fertility, they suggested stress caused by a shifting body clock or physical exertion could explain the findings.
Dr Gaskins said shift work could cause a reduction in fertility through “disruption in circadian rhythm that’s affecting normal hormone production and menstrual cycling, particularly for women who switch between day and night time work”.

She said it was difficult to say why jobs involving heavy lifting might reduce fertility, but suggested the body’s response to repetitive physical stress could affect a woman’s ability to produce good-quality eggs.
More than 3.1 million people in the UK work nights, a figure which has risen in recent years, according to a study by trade union TUC.

Women account for more than two thirds of the growth, according to the study, following an increase in night shifts worked by care workers and nurses.

We already know that physical exertion and stress can inhibit the female reproductive system and make periods less regular or even absent,” said Channa Jayasena, a senior lecturer in Endocrinology at Imperial College London.“Workers are increasingly moving away from a traditional 9 to 5 model, and we still know very little about how this could affect our health.

The participants, who had an average age of 35, were part of an ongoing Harvard study looking at the factors that might affect fertility called Environment and Reproductive Health (EARTH), which started in 2004.
Nine in 10 worked normal office hours, while 22 per cent said their jobs were moderately to very physically demanding and 40 per cent of women reported lifting or moving heavy objects at work.

Among women with physically demanding jobs, a greater difference in the number of eggs ready to be fertilised emerged between women who were overweight or over 37 years old and those who had a healthy weight or were younger.

Dr Jayasena said the study, published in the journal Occupational and and Environmental Medicine, was too small to rule out the potential impact of varying circumstances such as social conditions and diet.

Ying Cheong, Professor of Obstetrics and Gynaecology at the University of Southampton, told The Independent the research was “useful and interesting”.